In order to secure the bioequivalence when a pharmaceutical preparation having different amounts is administered at the same dose, there was issued “Guideline for Bioequivalence testing of Oral Solid Dosage Forms with Different Content” (Notification No. 64 of the Evaluation and Licensing Division, PMSD dated Feb. 14, 2000), by which it has been required that a pharmaceutical preparation having different amounts should be equivalent in dissolution profile in test solutions such as buffers of pH 1.2, 3.0 to 5.0 and 6.8 (which correspond to the pH values of the stomach, the intestine and the oral cavity, respectively), water, and saline solution, etc.
For medicaments showing a good solubility in water, it is easy to prepare such a preparation having equivalent dissolution profile even in different amounts due to their water solubility. On the contrary, for medicaments containing as an active ingredient a slightly water-soluble compound, it has been difficult to prepare a pharmaceutical preparation having equivalent dissolution profile even in different amounts, because such an active ingredient shows low affinity to water, etc.